JPS6196699A - Electronic ballast circuit for fluorescent lamp - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to ballast circuits for fluorescent lamps or other gas discharge lamps. In particular, the present invention applies to general 60Hz
It involves an electronic ballast circuit that energizes a fluorescent lamp at a high frequency from a power source.

BACKGROUND OF THE INVENTION As used herein, the term "fluorescent" is intended to include other gas discharge lamps, such as high intensity discharge lamps. These lamps are known to operate efficiently at frequencies higher than 60Hz. Typically such frequencies range from about 15 KHz to 100 KHz. The prior art suggests many electronic ballast circuits capable of operating at high frequencies, and there have been commercial attempts to provide such electronic ballasts.

The problem that the invention seeks to solve In order to obtain a long life in fluorescent lamps designed to operate at high frequencies, it is necessary to regulate the lamp current beyond what was thought necessary in early ballast circuits. I recently found out that I have to. There is one problem when trying to obtain highly regulated lamp currents. This is because, in the case of residential or commercial ballasts, the only power source that can actually be used is a common 60 Hz AC power source. 60Hz power supply is actually 120H
Even when rectifying the aftermath to supply z, the amplitude of the voltage supplied to the power transformer that normally energizes the lamp load varies considerably. It is undesirable if this amplitude change affects the supplied lamp current, as such changes may shorten the useful life of the lamp.

A measure or factor sometimes used by lamp manufacturers to define or define ballast characteristics to ensure long lamp life is "crest factor." this is,
It is defined as the ratio of the peak amplitude of the lamp current to the r m s value of the lamp current.

Most lamp manufacturers require that solid state ballasts operating at high frequencies have a crest factor of less than 1.6 for at least some lamps. One reason why a desired value of crest factor cannot be obtained in known electronic ballast circuits is that the voltage becomes Ov between peaks of the full-wave rectified power supply voltage. (This period between the peaks or peaks of the rectified voltage when the voltage becomes Ov, or when the voltage becomes surplus voltage when using an auxiliary power source, is called the "peak" period. Even when energy is stored using a standard DC voltage source (e.g., a capacitor), such systems do not require the use of unreasonably large value components such as auxiliary filters or oversized components. Without this, it is difficult to obtain a crest factor of less than 1.6, and some of the primary objectives of solid state ballasts, which are to reduce component size and increase operating efficiency, are not achieved.

In electronic ballasts, the crest factor can be improved simply by adding a large filter to the full-wave rectified power supply voltage, but this adds costly and bulky components and reduces the overall ballast efficiency is reduced.

Means for Solving the Problems Therefore, the main object of the present invention is to provide an electronic ballast circuit for a fluorescent lamp, which adjusts the lamp current so that the crest factor of the lamp current is less than 1.6. The purpose is to provide circuits. Yet another object of the invention is to provide a ballast circuit of the type described above without adding costly and bulky filter components to filter the power supply voltage.

The circuit of the invention comprises a half-bridge inverter circuit configured to resonate at a predetermined high frequency. A negative feedback circuit senses the lamp current and changes the excitation frequency of the lamp circuit to adjust the lamp current. In particular, the frequency response of this feedback circuit is large enough to respond to amplitude changes in the supply voltage such that the lamp current has a crest factor of less than 1.6. adjusted to a high degree sufficient to reduce the

OPERATION In the embodiment shown below, the lamp current is sensed;
A signal representative of lamp current is generated.

The feedback loop includes a variable frequency oscillator that generates a gating signal for the inverter's semiconductor switches and thus determines the operating frequency of the inverter. Therefore, the inverter circuit itself, also referred to as resonant amplifier pRJ, is driven at a predetermined controlled frequency, which frequency is preferably in the range slightly higher than the actual resonant frequency of the inverter. The lamp current controls the frequency of the inverter,
When an increase in lamp current is sensed, the operating frequency is increased, which reduces the gain of the resonant amplifier and reduces the voltage applied to the lamp circuit. That is, as the driving frequency of the inverter increases, the response of the inverter, ie.

The "gain" is reduced. In this way, the lamp current can be adjusted to obtain the desired crest factor described above.

Other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 10 generally indicates a thyristor/capacitor bridge circuit. This circuit consists of a first and a second thyristor (silicon controlled rectifier) 1
1.12, which are connected in series to the aftermath rectifier circuit 13.

This rectifier circuit takes standard 60 Hz line power and converts it to a 120 Hz full-wave rectified output signal, which is shown in ideal form in curve 1 of Figure 2. . □ The bridge circuit 10 also includes first and second balanced capacitors 16,17, which are connected in series to form the two legs of the bridge. The diagonal branch trunk of the bridge includes a power transformer 20, indicated generally by the reference numeral 20, whose output is connected to a lamp, including a gas discharge lamp, such as a fluorescent lamp, indicated schematically at block 21. Connected to load circuit.

The inductance of capacitors 16 and 17 and transformer 20 (including the reflected impedance from the load) form a resonant circuit when thyristor 11.12 is conducting.

The thyristors 11, 12 are activated "on" by a signal sent through a pulse transformer indicated generally by the reference numeral 23. This transformer 23 has a primary winding 24
, the primary winding of which is driven by a timing/feedback control circuit 27. The transformer 23 also includes first and second secondary windings 25,26, which are connected to the primary winding 24 of the transformer 23.
The thyristor 11 is made conductive so that when the current flows in the direction of , the thyristor 11 becomes conductive, and when the current flows in the opposite direction to the primary winding 24, the thyristor 12 becomes conductive.
．． Each of the gate lines is connected to 12 gate lines.

The timing signal for timing/feedback control circuit 27 is provided by zero-crossing detection circuit 28, which receives the signal from the secondary winding of power transformer 20.

This signal is shown as an x-cross and is sent to the zero crossing detection circuit 28.
generates a pulse every time the polarity of the load current reverses.

The signal labeled R is representative of the lamp current and is generated within the lamp circuit. This signal R is a signal of a certain level (not a sinusoidal signal), and its magnitude represents the value of the high frequency lamp current averaged over the number of cycles.

2, when the thyristor 11 conducts, the capacitor 16 is at least partially discharged and the arrow 1. A current indicated by flows through the thyristor 11 and then through the primary winding of the transformer 20 from its positive terminal to its negative terminal and from there through the capacitor to ground. transformer 20
Since the capacitors 16 and 17 form a resonant circuit, the current generator reverses the polarity according to the resonant frequency of the circuit, and then opens the gate so that the thyristor 12 conducts, allowing the current to flow in the direction of the arrow . flows.

At this time, thyristor 11 is non-conductive.

Thus, the frequency (which is, for example, 20kHz)
A high frequency current oscillating in the range from 50 kHz to 50 kHz) is generated in the lamp circuit and coupled to energize the lamp load. As a result, the positive half of the symmetrical waveform cursed by the output of the power transformer 20 is shown in an ideal form by curve 2 in FIG.

The envelope of the waveform is shown in phantom at reference numeral 30 as a series of peaks. This waveform corresponds in frequency to the rectified 120 Hz line voltage shown in curve 1,
generally have the same shape. The lamp current goes to zero when the power supply voltage goes to zero during the mountain period. A storage capacitor may be used to provide excess voltage during peak periods, the envelope in this case being as shown at 33 in curve 2. In any case, the crest factor of the lamp current is undesirably high because the lamp current generally follows a similar envelope.

In order to explain in more detail the operation of the current regulation function of the circuit of FIG. 1, the individual periods of the lamp current are shown in ideal form and on an extended time scale in curve 3 of FIG. ing. This curve is in the form of a sine wave, but as mentioned above, the peak-to-peak value of this wave is based on the magnitude of the rectified power supply voltage.

Referring now to FIG. 1, zero-crossing detection circuit 28 generates a signal at a time indicated by reference numeral 34 in FIG. 2 when current I or I2 passes through value O. At this time, the timing part of the control circuit 27 is indicated by the arrow tD on the curve 3.
forming a constant time delay shown schematically in . Signal R
The thyristor to be fired is triggered at the end of time tD if the lamp current, expressed by the value , corresponds to a predetermined or reference current value representing the desired lamp current. If the value of the signal R is greater than a predetermined reference value, indicating that the lamp current is greater than the desired value, the feedback control circuit 2 (7) proportionally delays the timing pulse, e.g. , the thyristor that should be gated will not be gated until 1 hour.This reduces the energy coupled into the resonant circuit and therefore the voltage applied to the power transformer 20. On the other hand, if the value of the signal R is smaller than the reference signal, this indicates that the lamp current is smaller than the predetermined value, and as shown at t2 of curve 1, the thyristor trigger time is advanced and the power transformer 20 is The coupled energy is increased because the thyristor is energized earlier in the inverter current cycle.
.

The response time of the feedback control circuit for the system of FIG. 2 is relatively slow, ie, several tenths of a second. In other words, one 3 db point of the frequency response characteristic of the feedback circuit is about 2-5 c/s. As a result, the amplitude of the voltage applied to the lamp circuit and the amplitude of the lamp current vary according to the envelope of the voltage waveform shown in curve 2. The resulting lamp current crest factor is undesirable based on the standards set by lamp manufacturers for lamp longevity, as explained above. In particular, curve 2 where the peak voltage becomes O
The envelope line of the signal indicates the peak lamp current, and I RMS
When the arrow indicated by indicates the effective value (rms) of the lamp current, the nominal value of the crest factor is in the range of 2.0 to 3.0.

FIG. 3 shows a preferred circuit for reducing the amplitude variation of the voltage applied to the lamp to adjust the lamp current and improve the crest factor of the lamp current. To facilitate comparison with the circuit of FIG. 1, components of the circuit of FIG. 3 having similar functions to those shown in FIG. 1 are designated with Il+ in front of the corresponding reference number. . Therefore,
An inverter in the form of a half-bridge circuit is shown generally at 110. This inverter includes first and second semiconductor switches 111.1.12.

Although the illustrated control switch is a MOSFET, other semiconductor switches may be used. MO5 has a high frequency response and can increase the inverter frequency, which reduces the size of other components.
A FET transistor was selected. The nominal operating frequency of the inverter in FIG. 3 is between 50 and 100 kHz;
The nominal resonant frequency is 50 kHz. MO5FE
The T transistor is suitable for this application, as will become clear from an understanding of this circuit, compared to the MOSFET.
) - transistor is turned on (i.e., conducting) when no forward current flows in the branch in which it is placed and turned off when forward current flows. This makes it easier for MOSFET transistors to turn on and off than, for example, bipolar transistors.
This makes it suitable for applications with a quick off time.

Furthermore, explaining FIG. 3, the inverter circuit 110 is
The other branch includes capacitors 116 and 117. To energize the inverter circuit 110, a 60Hz line voltage is connected across the rectifier bridge circuit 113, whose output is .

The signal is sent to an inverter circuit 110 as shown.

Primary winding 120 of a power transformer, generally designated 120
A is connected between the common connection point of the transistors 111, 112 and the common connection point of the capacitors 116, 117, ie the power transformer 120 is connected to the diagonal branch of the bridge circuit 110. The first secondary winding 120B supplies a lamp load circuit 121 which includes several configurations of fluorescent lamps or other gas discharge lamps, such as high intensity discharge lamps. A capacitor 122 is connected across this secondary winding 120B.
are connected to form a capacitive reactance that combines with the inductive reactance of the transformer 120 and defines the resonant frequency of the inverter. this is.

In the example shown here, it is approximately 50 kHz.

Transistors 111 and 112 are triggered at mutually exclusive times by a drive transformer 123 whose primary winding 124 is connected to the output of a logic/frequency control circuit 127 . Also, the first secondary winding 125 of the transformer 1 23 is connected to the gate of the transistor 11 and its second secondary winding 126 is
Connected to the gate of transistor 12 as shown. The details of the logic/frequency control circuit 127, described with reference to FIG. 4, are similar to the logic/feedback control circuit 27 of FIG. 1 in that it adjusts the value of lamp current in response to a signal representative of the lamp current. . However, circuit 127 does this in a different manner. For more details, please refer to the times wr! 27 cooperates with the bridge 11'O to take advantage of its frequency response characteristics and control the operating frequency of the bridge in relation to its resonant frequency to produce the overall desired output, or "gain". and adjusts the current. This is clear by referring to No. 51. In FIG. 5, reference numeral 135 is a curve showing the relationship between frequency and gain of an inverter circuit, sometimes referred to as a "resonant amplifier." In this regard, the resonance of the amplifier is primarily defined by the capacitor 122 and the leakage inductance of the power transformer 120, as discussed above.

Referring to FIG. 5, it is clear that the resonant frequency of the inverter is designated FR and that as the operating frequency increases above this resonant frequency, the gain of the inverter decreases. Furthermore, the gain decreases monotonically, but the resonant frequency F
It is clear that it is not necessarily linear between R and frequency F.

As can be seen, the one frequency control circuit 127 senses the average lamp current and generates an output signal which is sent to the transformer 123 to gate the transistors 111 and 112 during alternate half cycles. open. The frequency of this gate actuation or trigger signal is increased as the lamp current increases, and the voltage applied to the lamp load circuit at secondary winding 120B is decreased, reducing the lamp current.

Returning to FIG. 3, the surplus voltage is supplied to supply energy between the peaks of the full-wave rectified 120 Hz power supply voltage.

, this surplus voltage circuit includes a diode 136.

Its cathode is connected to the positive output of the full-wave rectifier bridge circuit 113 and its anode is connected to the storage capacitor 1
37. Diode 136 and capacitor 13
The connection point with 7 is the inductor 138 and diode 13
9 is connected to the connection point of transistors 111 and 112, which connection point is connected to the primary winding 1 of power transformer 120.
It is also an input terminal to 20A. Diodes 139 and 1
The half-wave rectifier formed by 40 provides a voltage equal to half the peak supply voltage and allows capacitor 137 to be charged from the high frequency output of the inverter circuit rather than the line supply, thereby minimizing line current distortion. while maintaining a high input power factor. Simply put, capacitor 137 is relatively large in order to store sufficient energy. This capacitor is charged via diode 139 and inductor 138, and when the amplitude of the output voltage of bridge circuit 113 falls below the voltage level stored in capacitor 137, diode 136 is charged.
It discharges after passing through. As shown, diode 139
A diode 140 may be connected between the transistor 112 and the transistor 112 .

Regarding the signal input to the logic/frequency control circuit 127,
A first input signal is derived from a secondary winding 141 of transformer 120, which secondary winding is connected to one or more windings in load circuit 121.
Connected to the filament circuit of the second lamp. A current transformer, indicated generally at 142, senses the current flowing into the load of secondary winding 141 and produces a signal ei on line 143 representative of the lamp load current. A further lamp filament is energized by the secondary winding 144. A further secondary winding 145 receives a signal e representative of the lamp voltage.

occurs. This signal eo is also sent along line 146 to logic/frequency control circuit 127 and is used to limit the lamp voltage as described in more detail below. A further secondary filament winding of the transformer 120 is shown at 155 and its output lead 156 is connected to the high voltage secondary with a starting capacitor 157.

The first and second resistors 148 and 149 are the transistor 11
Connected in series across resistors 148 and 112 to form a voltage divider, a signal representing the amplitude of the supply voltage appears at the junction of resistors 148 and 149. This signal is routed along lead 150 to logic/frequency control circuit 1.
27 and is used to provide protection against power supply overvoltages.

Current transformer 151 senses the current flowing through the primary winding of transformer 120 and includes a secondary winding 152 . line 153
The signal is designated ip, which represents the phase of the load current. this is.

along line 153 to the input of logic/frequency control circuit 127.

The logic/frequency control circuit output leads are 161 and 16
2, these are the primary winding 1 of the transformer 123.
It is directly connected to 24 terminals.

The power of the logic/frequency control circuit 127 is typically 163
is derived from a conventional bridge rectifier circuit shown at , which is capacitively connected to the line voltage and produces an output signal on line 164. This output signal is connected through a general voltage regulation circuit 165 to generate logic/control power for circuit 127. As is generally the case, Zener diode 164A and filter capacitor 164B are also connected as shown.

Now, FIG. 4 shows the logic/frequency control circuit 127 in a functional block diagram. Power transformer 120-2
Also shown is the next winding 145 and the lead 146 on which the signal eo appears. The signal eo represents the lamp voltage,
It is connected to a summing connection point 171 via a bridge rectifier circuit 170. Similarly, a signal ei representative of the lamp current generated in line 143 from current transformer 142 is connected via bridge rectifier circuit 172 to summing node 173 .

The other input of summing junction 171 is the signal es generated by the star 1-circuit surrounded by dotted line 175. Start circuit 175 starts line 1 when power is turned on and voltage is sensed at the output of low voltage regulator 165.
Operated by a 65A voltage signal. The start circuit includes a differentiating circuit 175A, which is an operational amplifier 175.
A negative input is provided to B, and the output of the amplifier is inverted by inverter 175C. The start circuit produces an output voltage for a predetermined period of time, as shown graphically in FIG.
decreases to v. The purpose of the start circuit 175 is to force the operating frequency to a high value during startup to allow heating of the lamp filament during the time before voltage is applied to the lamp. The output of summing node 171 is sent via filter 176 and diode 177 to the input terminal of voltage controlled oscillator 178. The output frequency of voltage controlled oscillator 178 increases with increasing input voltage.

The other terminal of summing junction 173 is received from the output of the phase detection circuit surrounded by dotted line 179. One input of this phase detection circuit 179 is.

It is received via line 153 from current transformer 151 and represents the phase of inverter current ip. Phase detection circuit 1
The other input signal at 79 is the drive signal on line 161 connected to the primary winding of drive transformer 123. This signal represents the phase of the voltage across the primary winding 2 and determines the triggering of the semiconductor switches 111, 112, as described above.

This signal is sent to a first Schmitt trigger circuit 180, squared, and sent to an ant game 1-182 via a differentiation circuit 181. The above signal ip is the second
Schmitt trigger circuit 183 and the other input of AND gate 182.

Phase detection circuit 179 is shown schematically in FIG. When the driving frequency of the semiconductor switch is near the resonant frequency F of the resonant inverter amplifier, the phase detector 179
The output signal of is a positive voltage. When the operating frequency of the inverter increases above the resonant frequency, indicating that the current ip lags the voltage ep, the output voltage becomes O. As the operating frequency of the inverter approaches or falls below the resonant frequency, the phase angle of the current advances and the output voltage increases. This output voltage is at the summing junction 173I
The output of the addition connection point 173 is sent to the filter 18
5 and a diode 186 to the input of a voltage controlled oscillator 178.

OPERATION As previously discussed, the frequency of voltage controlled oscillator 178 determines the operating frequency of the inverter. As this frequency increases from the resonant frequency, the gain of the inverter decreases continuously. At the time of starting, the start circuit 175 outputs the signal e.
This signal is transmitted to the connection point 171 and the filter 176.
and via diode 177 to the input of voltage controlled oscillator 178, setting the operating frequency to a high value. Therefore, the lamp voltage is at a low level until the filament is heated. At this time, the output signal of the start circuit 175 is O
Under normal conditions, the applied voltage of the lamp circuit increases as the frequency of the voltage controlled oscillator 178 decreases, which causes the semiconductor switch 1111
12 drive frequencies are reduced.

When the starting voltage begins to ramp down, at the end of a predetermined time period denoted T1, the drive frequency of the inverter decreases towards the resonant frequency and the voltage applied to the lamp increases correspondingly. START - As the voltage ramps down and the frequency of the inverter decreases, the applied voltage of the lamp increases, causing the signal eo%t'l on line 146 to be applied. The voltage applied to the lamp continues to increase until either the lamp lights up or the signal eo increases enough to limit the reduction in drive frequency.

When the lamp is switched on, the signal eO decreases due to the decrease in lamp voltage and, as mentioned above, the other summing junction 17
The signal ei representing the lamp current sent to the lamp 3 becomes the control signal. As mentioned above, the driving frequency of the inverter is typically in the range above the resonant frequency. If the drive frequency decreases towards the resonant frequency, the output of the phase detection circuit 179 is connected to the rectifier 17 at the summing junction 173.
2 and prohibits operation below the resonant frequency.

Assuming normal operation, ie, the operating frequency of the inverter is higher than the resonant frequency and the output signal of the phase detection circuit 179 is Ov, the output signal of the rectifier 172 (representing the lamp current) becomes the control signal. As the lamp current signal increases, the frequency of the voltage controlled oscillator also increases and the gain of the inverter is decreased. On the other hand, as the signal representing the lamp current decreases, the frequency of voltage controlled oscillator 178 decreases and the gain of the inverter circuit increases. The lamp current is thus regulated. When the operating frequency of the inverter becomes very low, ie, below the resonant frequency of the inverter, the output signal of the phase detection circuit 179 increases, thereby limiting the lower operating frequency of the voltage controlled oscillator 178. Therefore.

Phase detection circuit 179 defines the lower limit of the inverter's operating frequency range.

If the voltage applied to the lamp circuit increases beyond its normal operating range (as would happen if the lamp burns out or is removed), the signal eo at input 146 increases and the voltage controlled oscillator 178 frequency to a higher frequency, thereby reducing the inverter gain and avoiding overvoltage conditions. diode 177.186
The function of is to ensure that a high output signal from either summing node 171 or 173 effectively drives voltage controlled oscillator 178. That is, the two output signals of the summing junction are not added. Rather, the larger signal controls the operating or driving frequency.

The characteristics of voltage/frequency converter 78 are such that as the input signal increases, the frequency of the output signal also increases. To explain the effect of increasing the frequency of the signal connected to drive transformer 123, reference is made to response characteristic 135 in FIG. As the operating frequency increases, the gain decreases and the amplitude of the voltage across the secondary winding 120B of the transformer 120 decreases, thereby decreasing the lamp current. The frequency response of the circuit of Figure 4, also referred to as a feedback control circuit or frequency control circuit, is configured such that its -3 db frequency point is approximately 5 kHz relative to the 50 kHz resonance frequency (F in Figure 5). By doing so, it is possible to obtain a wave φ forgetting rate of less than 1.6. Thus, not only is the lamp current regulated, but it is also made relatively insensitive to variations in the supply voltage. - By way of example, referring to FIG. 6, curve 1 schematically shows the envelope of the voltage applied to the primary winding 120A of the power transformer 120, but it is possible to change the driving frequency of the inverter. Due to the regulating action achieved by , the output voltage of transformer 120 is as shown in ideal form by curve 2 in FIG.

In the example shown, the operating frequency range was above the resonant frequency of the inverter amplifier, but it will be obvious to those skilled in the art that the system described above can be modified to operate in other parts of the frequency response, e.g., before the resonant frequency. Probably.

Having thus described the preferred embodiments of the invention in detail, it will be apparent to those skilled in the art that various changes may be made to the circuitry described above and equivalent components may be substituted while still carrying out the principles of the invention. Dew.

It is therefore intended that all such modifications and substitutions be included within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of an electronic ballast circuit using negative feedback to regulate lamp current; FIG. 2 is a ninth ideal diagram illustrating the operation of the circuit of FIG. FIG. 3 is a circuit diagram and partial block diagram of an electronic ballast for a gas discharge lamp constructed in accordance with the present invention. FIG. 4 is a circuit diagram and partial block diagram of the timing/frequency control circuit of FIG. 3, FIG. 5 is a graph showing the gain versus frequency characteristics of the inverter circuit of FIG. 3, and FIG. 4 is a graph showing an ideal waveform showing the operational performance of the circuit shown in FIG. 3; 10... Thyristor/capacitor bridge circuit 11.
12...Thyristor 13...Full wave rectifier circuit 16.17...Capacitor 20...Power transformer 23...Pulse transformer 24...Primary winding 25.26...Secondary Winding 27...timing/feedback control circuit 28...
...Zero crossing detection circuit

Claims (20)

[Claims] (1) An electronic circuit for energizing a lamp circuit comprising at least one gas discharge lamp from a power supply whose voltage amplitude varies over time, the electronic circuit comprising: inverter circuit means for receiving power from said power supply; and the inverter circuit means includes first and second control switches, each of which opens a gate to conduct during alternating cycles of the inverter frequency to provide power to the lamp circuit. sensing circuit means for generating a high frequency electrical signal for supplying a lamp current, further comprising sensing circuit means for generating a control signal indicative of lamp current, and further for controlling gating of said control switch in response to said control signal; feedback control circuit means for adjusting the voltage to a predetermined value, and the feedback control circuit has a frequency response defined by a cutoff frequency sufficient to enable it to respond to amplitude changes in the power supply voltage. 1. An electronic circuit, characterized in that it is capable of reducing amplitude variations in the supplied lamp voltage and lamp current. (2) said power source includes rectifier circuit means for receiving power from a 60 Hz input line and generating power for said inverter circuit, and the output of said rectifier circuit means being sufficient to supply energy to said inverter circuit means; a source of surplus voltage which at times stores energy and supplies energy to said inverter circuit means when the output of said rectifier circuit means is insufficient to supply energy to said inverter circuit means; An electronic circuit according to claim (1). (3) the inverter circuit means comprises a resonant circuit having a resonant frequency, the output of the resonant circuit is connected to the lamp load circuit to energize the lamp; and the feedback control circuit means comprises a resonant circuit having a resonant frequency; adjusting the output of the resonant circuit in response to the control signal representative of the lamp current during normal operation while varying the conduction frequency of the first and second control switches in relation to the resonant frequency of the circuit means; An electronic circuit according to claim 2, comprising means for adjusting the lamp current and reducing the crest factor of the lamp circuit. (4) the range of operating frequencies of said inverter circuit means determined by said feedback control circuit means is higher than the resonant frequency of said inverter circuit means, said feedback control circuit means comprising variable frequency oscillation circuit means; The circuit means, in response to said control signal,
4. An electronic circuit according to claim 3, wherein the frequency of the drive signal is increased to open the gate of the control switch when the lamp current increases above a reference value. (5) According to claim (4), the control switch is a semiconductor switch connected in series and energized to conduct at a mutually exclusive time period. electronic circuit. (6) The electronic circuit according to claim (5), wherein the semiconductor switch is a MOSFET transistor. (7) The inverter circuit means includes a resonant circuit having a resonant frequency, and the feedback control circuit means includes:
Claim 1, further comprising a variable frequency circuit for energizing the control switch at a controlled frequency, the variable frequency circuit changing the driving frequency of the control switch in response to the control signal. The electronic circuit described in . (8) The feedback control circuit means is characterized in that the normal operating frequency of the variable frequency circuit means is higher than the resonant frequency of the inverter circuit means; and in response to a signal representative of the phase of the applied lamp voltage, the variable frequency circuit means generates an output signal when the operating frequency approaches the resonant frequency of the inverter to lower the operating frequency below the resonant frequency. An electronic circuit according to claim 7, comprising phase detection circuit means for frequency limiting. (9) in response to the initial application of power, generating an output signal causing said variable frequency circuit means to generate a drive frequency higher than said normal operating frequency to drive said lamp filament; Claim 8 further comprising start circuit means for reducing the gain of said inverter circuit means during an initial start time sufficient to allow heating.
) Electronic circuits described in paragraph (10) sensing the lamp voltage, increasing the output frequency of the variable frequency circuit means when the lamp voltage exceeds a predetermined value, and decreasing the gain of the inverter circuit means when the lamp voltage is higher than a desired value; An electronic circuit as claimed in claim 9, further comprising voltage sensing means. (11) At least 1
In an electronic ballast circuit for energizing a lamp circuit including two gas discharge lamps, the ballast circuit includes inverter circuit means including first and second control semiconductor switches, the semiconductor switches being connected to the first and inverter circuit means in circuit connection with a second capacitor to form an inverter bridge circuit, the inverter circuit means being connected to a diagonal branch of the inverter bridge circuit and having a secondary winding connected to the lamp circuit. and variable frequency circuit means for generating an output signal connected to said first and second control switch means, said power transformer means for energizing said first and second control switch means; variable frequency circuit means each conducting during alternating cycles to generate a high frequency signal for energizing said power transformer; and sensing lamp current and controlling said variable frequency circuit means for operation thereof. An electronic ballast circuit comprising sensing circuit means for varying the frequency in response to changes in the lamp current and for controlling the lamp current by varying the gain of the inverter circuit means. (12) A power supply circuit connected to the power supply voltage, which stores energy from the power supply when the power supply voltage is relatively high, and supplies power to the inverter circuit means when the power supply voltage is relatively low. A circuit according to claim 11, further comprising storage circuit means. (13) further comprising a capacitor circuit-connected to a secondary side of the power transformer, the inductance of the power transformer and the value of the capacitor at least partially determining a resonant frequency of the inverter circuit means; and said variable frequency circuit means triggers said first and second switches to drive said inverter circuit means at a frequency higher than said resonant frequency, whereby the gain of said inverter circuit means is equal to said drive frequency. 11. A circuit according to claim 10, wherein the circuit is adapted to vary as a function of . (14) The sensing circuit means generates a signal representative of the lamp current, and when the lamp current increases, the variable frequency circuit means increases to decrease the gain of the inverter circuit and decrease the lamp current. Claim No. 1
The circuit described in section 3). (15) The variable frequency circuit means and the sensing circuit means include feedback control circuit means having a frequency response sufficient to adjust the lamp current to the fundamental frequency of the power supply voltage. The circuit described in (14). 16. The circuit of claim 15, wherein the feedback control circuit means has a frequency response that defines a cutoff frequency that is at least ten times higher than the fundamental frequency of the power supply voltage. (17) The feedback control circuit means further comprises a limiting circuit means for detecting when the operating frequency of the inverter approaches the resonant frequency and limiting the lower limit range of the operating frequency of the inverter circuit means. A circuit according to claim (16). (18) The limiting circuit means compares a first signal representing the phase of the lamp current with a second signal representing the phase of the applied lamp voltage so that the operating frequency is equal to the resonant frequency of the inverter circuit means. 18. A circuit as claimed in claim 17, comprising a phase detector for determining the time of approach. (19) The feedback control circuit means further causes the variable frequency circuit means to operate at a higher frequency in response to the initial delivery of power, thereby:
19. The circuit of claim 18 further comprising starting voltage circuit means for reducing the gain of said inverter circuit means for a predetermined period of time sufficient to heat the filament of said lamp during starting. (20) further comprising means for sensing the voltage applied to the lamp and generating a signal representing the voltage, the signal representing the voltage of the lamp being sent to the variable frequency circuit so that the voltage of the lamp exceeds a predetermined value; The circuit according to claim 19, which increases the frequency of the inverter when the frequency of the inverter increases.